The causes of the most common type of high blood pressure, essential hypertension, probably begin to operate in childhood in the family setting. With increasing age, the prevalence of hypertension increases. The actual level of blood pressure in adults has been shown to be one of the strongest predictors of future level of blood pressure. Tracking of blood pressure has also been demonstrated in children - that is, persons with high normal blood pressure continue over time to have high blood pressure. Because of the variability of blood pressure measurement individuals can best be ranked by repeated measurements on separate occasions rather than repeated measurements on one occasion. This study is one of very few with repeat blood pressure measurements twice a year in children. Data have now been collected biannually for 2-5 years on children at school for height, weight, skinfold thickness and blood pressure. These children and their parents have also undergone extensive medical and psychological tests and completed nutritional questionnaires and given overnight urine specimens for sodium and potassium analysis. Multivariate analysis to examine predictors of tracking of blood pressure will be made in this final year of the study. This will allow definitions of the most appropriate strategies for primary prevention of hypertension.